1. Field of the Invention
The present invention relates to a monitor for measuring ultraviolet irradiance in a reactor vessel or in a conduit within which an ultraviolet light source is positioned for irradiating a liquid. More particularly, the present invention relates to an actinometric monitor that is removably supported at the wall of a flow conduit that contains a flowing liquid that is irradiated by ultraviolet light, or at the wall of a vessel that contains a liquid that is irradiated by ultraviolet light.
2. Description of the Related Art
Water disinfection reactors having ultraviolet light sources disposed within the water to be disinfected have been known for some time. The ultraviolet light deactivates pathogenic microorganisms without producing residuals or hazardous byproducts, and it avoids the need to use hazardous disinfection chemicals.
Generally, the output of ultraviolet lamps utilized in disinfection reactors diminishes gradually over time. Such diminution results from aging of the lamps and also from blockage of the light by deposits on the surfaces of the lamp housings. The deposits are typically dissolved minerals in the water that adhere to the surfaces of the quartz tubes or sleeves within which the ultraviolet lamps are usually housed, and the deposits either physically block the light path or they absorb ultraviolet light. As a consequence, the effectiveness of the disinfection process must be monitored by periodically determining the amount of ultraviolet light that actually passes through the water being treated.
Typically, ultraviolet-light-based disinfection reactors are equipped with photocells that are sensitive to ultraviolet light. The photocells measure relative changes in the ultraviolet fluence rate (or irradiance) within the flowing water. Changes in ultraviolet irradiance patterns in the reactor because of lamp aging, buildup of light-blocking deposits on the surfaces of the quartz sleeves, or changes in the ultraviolet transmittance of the fluid being irradiated, can be sensed by the photocells. But the photocells only indicate relative values of ultraviolet light irradiance at a particular location in a disinfection reactor.
In addition to their inability to directly determine the absolute value of the ultraviolet-light dose to which the water is subjected at a particular location within the reactor, the sensitivity of photocells decreases with use. Such decreases are caused by surface damage from ultraviolet light radiation and also by aging of the photocells. Accordingly, recalibration of the photocells is required at regular intervals, to assure that they can be relied upon to accurately monitor changes in the irradiance output from the ultraviolet light sources. Typically, the photocell sensors must be removed from the reactor and recalibrated by the manufacturer using a radiometer, which is a time-consuming and expensive procedure.
It is therefore an object of the present invention to provide an actinometer-based ultraviolet monitor that can measure the actual exposure of a liquid to ultraviolet light at a particular location in an ultraviolet light reactor vessel or conduit, and to provide a simple and inexpensive means to recalibrate photocell sensors, thus overcoming the deficiencies and limitations of the previous techniques.
Briefly stated, in accordance with one aspect of the present invention, an actinometric monitor is provided for measuring ultraviolet irradiance in a water disinfection ultraviolet reactor that includes an interiorly-positioned ultraviolet light source. The monitor includes a holder for selectively receiving one of a photocell-based ultraviolet light sensor having a surface positioned at a predetermined distance from the light source and an actinometric-solution-based ultraviolet light sensor having a surface positioned from the light source at the predetermined distance. The holder is adapted to be removably positioned in a holder sleeve extending outwardly from a wall of the reactor. A window that is substantially transparent to ultraviolet light is positioned between the light source and the holder to prevent contact between the holder and liquid to be treated by exposure to ultraviolet light within the reactor. A recess is provided in the holder and is positioned at a predetermined distance from the light source for removably receiving an actinometric-solution-containing cuvette.